Вот код, который я добавляю, и он работает
$activities = [];
foreach ($activity_result as $activity) {
if(in_array($activity->user_id, $userFriendIds))
{
$activitydetail = Activity::where('id', $activity->id)->with('joins')->get();
} else {
$activitydetail = Activity::where('id', $activity->id)
->where('activity_privacy_visible', 0)->with('joins')->get();
}
$activities = array_merge($activities, $activitydetail->toArray());
}